Get first image in a post url

Avg Bid (USD)
$9 / hr
Project Budget (USD)
$2 - $8 / hr

Project Description:
I want a way to get the url of the first image in a post even this image is not hosted on my website, I want it to be done to post it in facebook open graph protocol

for example this thread :

I want a way to autmoatically put the url of the image :
in Facebook OG like :

Hours of work: Unspecified Project Duration: < 1 week Skills required:
Javascript, PHP, Software Architecture, vBulletin
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